At present, in fabricating a semiconductor device, a capacitive-coupled plasma processing apparatus is often adopted to generate plasma of reaction gas for performing processes such as etching and depositing on the substrate.
FIG. 1 shows an existing capacitive-coupled plasma generator, in which at least one pair of planar electrodes, i.e., a first electrode 210 and a second electrode 220, is arranged in parallel in a vacuum reaction chamber 100 of the plasma generator, and a substrate 300 to be etched is placed on a supporting holder 120 where the second electrode 220 is provided; optionally, radio frequency power is applied on the second electrode 220 and the first electrode 210 is grounded to generate a radio frequency electric field for ionizing the reaction gas that is introduced into the reaction chamber 100 and generating plasma to be used for etching.
However, the uniformity of the electric field distribution in the reaction chamber of the prior art is far from ideal. The difference in the actual structures of the two electrodes and the grounded sidewall will lead to bend of the electric field lines, causing the whole radio frequency electric field in the reaction chamber 100 to be non-uniform.
As shown in FIG. 1, the electric field lines 230b located at the middle positions above the second electrode 220 are distributed uniformly; however, the closer to the side positions above the second electrode 220, the radio frequency electric field lines 230a are bent, and the greater the deflection angle of the electrode field lines 230a are and the more sparsely the electrode field lines 230a are distributed. Referring to the dashed lines in FIG. 1, they indicate the density distribution of the plasma at different positions above the second electrode 220. It can be seen that the density of the plasma of the reaction gas generated at the side position of the second electrode 220 is less than that at the middle position of the second electrode 220; and because the speed of etching or other processes on the substrate 300 is in positive relation to the density of the plasma, the non-uniformity of the etching or other processes on the substrate 300 would happen finally. For example, the etching or the other processes are done quickly in the center portion of the substrate 300 while slowly at the edge portion of the substrate 300. This has great influence on both the process control and the final quality of semiconductor device fabrication.